Core Contradictions in Local Connector Soldering

Industrial control boards are often integrated with through-hole connectors of 20 pins or more, with the spacing between their pins and surrounding heat-sensitive components such as BGAs, crystal oscillators, and EEPROMs being less than 3mm. If whole-board wave soldering is adopted, it will inevitably lead to cold solder joints on adjacent components or PCB delamination, while manual iron touch-up soldering makes it difficult to control the consistency of heat input. JJY Selective Wave Soldering, through independently programmable nozzles paired with precise X-Y-Z three-axis positioning, covers only the target pad area with the solder wave, shrinking the heat-affected zone to within 1.2mm.

Cooperative Design of Solder Wave Parameters and Fixtures

Our actual measurements found that when the solder pot temperature is set to 265℃, the solder immersion depth is controlled at 1.8mm, and the contact time is maintained at 3.2 seconds, the wetting angle of solder joints on gold-plated connectors on 0.5mm thick FR4 substrates is generally less than 25°. However, the prerequisite is that the fixture must have a double-sided pressing structure; otherwise, a 0.15mm micro-warpage of the PCB under wave impact will cause consecutive missed soldering on pins 3 to 5. The downward pressure of JJY's standard pneumatic pressure claw is set to 8.5N, paired with a height tolerance of ±0.03mm for the bottom support block, to ensure synchronous immersion soldering of the entire row of pins.

Matching Logic of Flux Spraying and Preheating

The copper thickness of connector pads usually reaches 70μm, with a stronger oxidation tendency than conventional pads. Therefore, a no-clean flux with a solid content of 38.5% must be used, and the spraying amount is strictly controlled at 12mg/cm². Paired with three-stage preheating at a chain speed of 1.1m/min: the first stage at 120℃ for 45 seconds is used for solvent volatilization, the second stage at 155℃ for 30 seconds completes flux activation, and the third stage at 185℃ for 20 seconds eliminates internal stress of the PCB. Any temperature deviation exceeding ±3℃ in any stage will cause solder joint icicles or bridging.

Key Points for Suppressing Post-Soldering AOI False Positive Rates

Connector solder joints are easily misjudged as insufficient solder by AOI systems due to the reflective characteristics of pins. We adjusted the solder wave generator angle of JJY's equipment to 13° and added a 0.3-second post-blow delay, so that a uniform arc-shaped solidification contour is formed on the solder joint surface. Then, paired with changing the AOI light source angle from 45° to 62° incidence, the false positive rate of this type was finally reduced from 17.3% to below 0.9%, while ensuring that X-ray inspection confirms the internal void rate is always below 12%.